Estrogen is an endogenous hormone which has a variety of significant functions in human physiology. Predominantly, this hormone affects the reproductive system of both males and females. For example, in the adult female, estrogen is integral in pregnancy and lactation processes. It also lowers the risk of heart attack and osteoporosis. In addition, the ratio of estrogen to androgens in pre-natal and early post-natal stages regulates sexual differentiation and proper formation of the appropriate reproductive organs. Estrogen has also been associated with increases in breast and uterine cell growth, i.e. cancer. In males, estrogen regulates sperm production, with abnormally high concentrations resulting in decreases in sperm count.
In recent years, there has been increasing concern over the exposure of human and wildlife populations to manufactured or naturally occuring chemicals which act to mimic the action of endogenous estrogen. These substances are derived from a variety of sources including pesticides, animal health products, plastics, combustion-by-products, and plants (phytoestrogens). Specific examples include zeranol, genistein, coumestrol, o,p-DDT, kepone, methoxychlor, zearalenone, dioxin, p-octylphenol, and bisphenol A. In general, this class of compounds has been termed environmental estrogens and has been implicated in a variety of disease states including gynecomastia (DiRaimondo et al., N. Engl. J. Med. 302, 1089, (1980)) precocious puberty (Comas, Lancet, 1299, (1982)), low sperm counts (R. M. Sharpe et al. Lancet, 341, 1392, (1993)), endometriosis (S. E. Rier et al., Fundam. Appl. Toxicol., 31, 423, (1993)), and breast cancer (M. S. Wolff et al., J. Natl. Cancer Inst., 85, 648, (1993)).